IL44577A - Separation of fatty mixtures into constituents of different melting points - Google Patents

Description

o'a'aia1? ni»3»iw nianyn tmsn nuiw "p 'n nnipj *Vya The sepaxation of fatty mixtures into constituents of different melting points HEMEL & CIE. GMBH C. 42660 The invention relates to a process for the separation of fatty mixtures into constituents of different melting points by the process of redistribution of water, in which the withdrawal of heat necessary for the cooling and crystallisation of the higher melting fatty fractions is obtained substantially by vacuum evaporation of an aqueous non-surface-active electrolyte solution in direct contact with the fatty mixture.

The separation of fatty acid mixtures or of fatty acid ester mixtures into components of different melting points by the water redistribution process is known from the U.S.

Patent Specification No. 2,800,493» According to this a mixture of solid and oily fat particles is converted by means of a wetting agent solution into a dispersion of solid and oily fat particles separated from one another, and this dispersion is separated by means of a solid-jacket centrifuge into an oily and an aqueous phase containing the solid fat particles in dispersion. The withdrawal of heat necessary for the crystallisation of the solid fat particles is obtained by cooling devices, especially scraper coolers. After the end of the separation process the wetting agent solution again obtained is returned to the process. The German Patent Specification No. 1,010,062 describes a corresponding separation process for fatty alcohols.

The essential disadvantages of the said processes consist in the high investment and operational costs for refrigerating machines and devices. In particular, the scraper coolers needed are expensive in construction and require constant attendance.

Furthermore, from the U.S. Patent Specification No.J,5^1»122 a process for the separation of mixtures of fatty materials into fractions of different melting points is known, which also operates according to the water redistribution process. However, in this case the cooling of the molten fatty mixture necessary for the crystallisation is obtained by vacuum evaporation of water. After the dispersion of the fatty mixture consisting of liquid and solid particles in a wetting agent solution is effected, the solid phase which has crystallised out is separated by filtration, while the oil dispersion passes through the filter. No complete separation of oil fractions and fat particles is effected by this method so that the fat particles have a relatively high iodine value and therefore a comparatively poor quality.

Further, a process is known from the German Patent Specification No. 1,915,298 for the separation of fatty acid, fatty alcohol or fatty acid ester mixtures into components of different melting points by mixing the molten mixture with an aqueous wetting agent solution, when the crystallisation of the solid fractions to be separated is obtained by evaporation of a part of the aqueous wetting agent solution under reduced pressure. Since the fats used are only incompletely and with difficulty degassed when they are fed into the crystallisation vessel, stronger development of foam occurs on addition of the wetting agent solution, owing to which the course of the process is considerably upset. Moreover, the wetting agent hinders the growth of the crystals, which again leads to difficul'^jps ' in the further separation of oily and solid phases.

It is the object of the invention during the carrying out of the redistribution process, on the one hand to avoid the high investment costs for the installation and the servicing of refrigeration and cooling machines and devices, especiall scraper coolers, and on the other hand, to improve the efficiency of the separation process and consequently the quality of the products obtained.

The present invention relates to a process for the separation of fat mixtures into, components of different melting points by the redistribution process, in which the withdrawal of heat necessary for the cooling and crystallisation of the higher meltj.ng fat fractions is obtained by vacuum evaporation of an aqueous phase in direct contact with the fat mixture, which is characterised by the following measures: (a) partial or complete melting of the fat mixture (b) addition of an aqueous non-surface-active electrolyte solution to the molten fat mixture and evaporation of a part of the water of the electrolyte solution by application of a vacuum, with simultaneous intensive mixing until the higher melting fraction is partly or completely crystallised (c) addition of wetting agent solution with dispersion of the liquid and solid fats, preferably while the vacuum is still maintained and the evaporation of water is continued until the separation temperature is attained (d) Separation of the dispersion by means of centrifuges into an oily phase containing the lower melting fat fractions and an aqueous phase containing the crystallised fat fractions in dispersed form separation of the higher meltin fat fractions from the aqueous phase by filtration or by melting up and subsequent centrifuging or allowing to settle In the preferred form of the process the aqueous electrolyte-containing wetting agent solution is partly or wholly returned to the process.

The process is suitable for the separation of many different types of fat mixtures, and in particular mixtures of fatty acids, fatty acid esters or fatty alcohols can be separated when the melting points of the components to be separated lie sufficiently far apart.

The separation of fatty acid mixtures into olein and stearin or fatty alcohol mixtures into oleyl alcohol and stearyl alcohol is of special technical importance o Correspond ingly, solid mixtures of fatty acid triglycerides can be separated at room temperature into lower and higher melting fractions* Such fatty acid triglyceride fractions are used for the proauction of edible fats*, It is not necessary for one of the components to be separated to be present as a liquid oil at room temperature. The process can also be successfully used when both fractions are solid and are simply sufficiently different in melting point.

The claimed process is carried out as (a) The fatty mixture provided for the separation is wholly or partly melted in a suitable heatable vessel, for example a stirred vessel, so that the temperature of the mixture lies above the intended separation temperature. It is also possible to precool the completely melted mixture in a conventional way,- for example in heat exchangers, so that a partial separation of the fat fraction to be separated has already occurred. In general a partial crystallisation at this stage is avoided for technical reasons and the temperature selected is somewhat above that of the crystallisation used. (b) The further cooling of the wholly or partly melted fat mixture is obtained by vacuum evaporation, and may be carried out in a batch process or continuously. An aqueous non-surface-active electrolyte solution is used as the liquid to be evaporated. This solution is brought into contact with the fat mixture under vacuum and with intensive mixing, and is kept under reduced pressure with the water vapour formed being constantly pumped off, until a viscous crystal slurry is formed by the crystallisation of solid fat from the fat slurry, which can barely be intermixed with stirring devices. The temperature hereby attained is denoted as the limiting temperature for the crystallisation. In this stage the evaporation of the water is greatly hindered owing to the insufficient mixing, so that the cooling speed Ϊ3 considerably decreased. and a further continuation of the process would be uneconomic.

If the batch process is' operated, the pressure in the stirred vessel is lowered by means of a suitable evacuation equipment. The vapour pressure of the water at the respective temperature is adjusted above the liquid, so that the cooling is effected without temperature jumps in the metastable area of the crystallisation along the vapour pressure curve of the water. In this region spontaneous seeding is largely avoided, andrelatively large crystals are formed which can easily be separated from the adhering oil phase.

The addition of the electrolyte solution is effected after evacuation of the vessel either discontinuously o continuously. The electrolyte solution may be passed in under the surface of the fat mixture, if desired, in finely divided form, owing to which an intensive and thorough mixing takes place at the same time.

In the continuous process a stirrer vessel cascade is suitably ised. Fat and electrolyte solution are fed into the first stirrer vessel of the cascade and then pumped from one stage to the next. Seen in the direction of flow of the streak of product, the pressure and therefore the temperature corresponding to the vapour pressure of the water decreases in jumps from vessel to vesselβ The jumps of temperature must be so small and consequently the number of stirrer vessels of the cascade must be so great that the crystallisation as in the batch process is effected in the metastable region and spontaneous seeding is avoided, in order to come as close as. possible to the "ideal crystallisation" attainable in the batch process along the vapour pressure curve of the water.

T e quantity of heat removed "by evaporation is/" · dependent on the heat capacity of the hatch, the lowering of temperature desired and the heat of crystallisation obtained. At least as much electrolyte solution must he added to the batch for the necessary reduction of temperature to be obtained and when the limiting temperature of the crystallisation is reached, a still stirrable and pumpable crystal slurry is present. As a rule, however, the amount of electrolyte solution added is equal to the water and wetting agent solution removed from the cyclic process., The amount of wetting agent solution to be separated from the cyclic process depends largely on the purity of the fats and is necessary for the removal of slime and dirt from the process, which affects the crystallisation and if it were not removed the iodine values of the solid components of the fats at the separation temperature would be steadily worsened.

The temperature of the electrolyte solution should % as far as possible be about equal to that of the fat charge.

The aqueous non-surface-active electrolyte solution used in the process contains about 0.1 to 10, preferably 0.5 to 2%. by weight of a water-soluble chloride, sulphate or nitrate of mono- to tri-valent metals, especially of the alkali, alkaline earth or earth metals „ Above all, additions of sodium sulphate, magnesium sulphate or aluminium sulphate have proved satisfactory. The total amount of electrolyte to be added depends on the fraction of electrolyte-containing wetting agent solution removed from the cycle at the end of the separation process. ' (c) After reaching the desired temperature , the v" uum can he removed and the amount of a wetting agent solution necessary for the dispersion of the liquid and solid fats may he added. The redistribution process is carried out under intensive mixing, when the oily fractions of the fat mixture are displaced from the surfaces of the crystallised fractions. .

The preferred variant of the process,, however, consists in inserting a part of the wetting agent solution before the desired separation temperature is reached. This is suitably done as soon as the limiting temperature of the crystallisation is reached, since the further addition of wettin agent leads to a liquefaction of the crystalline slurry. With maintenance of the vacuum the evaporation and cooling process can now proceed until the separation temperature intended is reached0 At the same time the redistribution process occurs and a watery dispersion is formed which contains both the oily and the crystallised fat fractions dispersed as particles separated from one another,, The wetting agent solution used is substantially the old dilution originating from the cyclic process, which is added to the possibly still fresh wetting agent as a replacement for the fraction of wetting agent separated. Difficulties through foam formation do not occur when the process is operated according to the preferred variant, i.e. when the wetting agent solution is introduced into the vessel still under vacuum. This is suitably effected by feeding in above the surface of the liquid, owing to which extensive degassing (removal of the dissolved air) is effected "before stirring in the fat/ele^jgolyte solution mixture. The fats inserted are besides degassed by the previous vacuum evaporation cooling* The water vapour developed during the continuation of the evaporation cooling is formed relatively densely under the -surface of the liquid and only has a very short distance to rise, so that owing to this no foam is formed.

In order to obtain a separable dispersion, the fraction of the aqueous phase at the end of the evaporation cooling amounts to 0.3 to 5 times, preferably 0.7 "bo 3 times the fat used. The losses arising from the cyclic process by discharging a part of the wetting agent solution, the so-called old dilution, are replaced, suitably after lifing the vacuum, by a corresponding amount of electrolyte solution for the' crystallisation and of fresh wetting agent.

Useful wetting agents are anionic or non-ionic water-soluble substances which lower the surface tension of the aqueous solution and thus cause a displacement of the oily components of the starting mixture from the surface of the crystallised fractions. The surface-active substances mentioned in the U.S. Patent No. 2,800,4-93 are useful as wetting agents, especiall compounds having alkyl residues having 8 to 18, preferably 10 to 16 carbon atoms in the molecule, for example soaps, alkylbenzene-silphonates, alkylsulphonates , fatty alcohol sulphates, sulphated reaction products of fatty alcohols having 1 to 10, preferably 2 to 5 mol of ethylene oxide and/or propylene oxide, fatty acid monoglyceride sulphates and so forth. The._said anionic wetting agents are preferably used as sodium sal¾Sj but in some cases also as potassium, ammonium, mono-, di- o tri-ethanolamine salts . Useful non-ionic compounds are, for example, the water-soluble products of addition of ethylene oxide to alkylphenols or fatty alcohols. The fat dispersion should contain 0.05 to 2, preferably 0.1 to 1 parts by weight of wetting agent to 100 parts by weight of solution. These data include not only the wetting agent dissolved in' the aqueous phase, but also the amounts of wetting agent dissolved in the oil or adsorbed on the surface of the solid components. (d) After cooling is effected and lifting of the vacuum, the dispersion of the fat fractions by means of centrifuges for example solid jacket centrifuges, or separators into an oily phase containing the lower melting fat fractions and an aqueous phase containing the crystallised fat fractions in dispersed form. Various types of centrifuge are suitable for this process, for example pipe centrifuges, plate centrifuges or scoop pipe centrifuges. The latter type, in which the phases are removed by scoop pipes from the centrifuge, has been found especially useful.

After running through the centrifuge the oily fat fractions, possibly after washing and drying - are conveyed to their intended destination. If necessary, a further separation process at lower temperature can follow, an oil being obtained with a correspondingly lower turbidity point. (e) The suspension of crystallised fat fractions coming from the centrifuge is separated by heating the suspension with melting of "the crystalline fat fractions and subsequent centrifugal separation or leaving to settle , for example separating boxes β It is also possible to filter off the crystallised fat fractions. The higher melting fraction of the fat mixture thus obtained, after passing once through the separatin process, has a very high purity* The recovered wetting agent solution is returned to the separating process as the so-called old dilution. It is of course necessary to remove a part of this solution continuously from ¾he cycle in order to avoid the accumulation of slimy impurities from the fats used, which may spoil the crystallisation as well as the qualify of the higher melting fat fraction. The thereby occurring loss of wetting agent must he compensated by addition of fresh wetting agent.

The loss of electrolyte occurring at the same time is replaced by the electrolyte solution supplied during the evaporation cooling, especially during the crystallisation. The process must further be controlled so that the losses of water occurring during evaporation cooling or by the withdrawal of wetting agent solution are compensated by the added electrolyte solution and fresh wetting agent solution.

The method of operation according to the invention a3 special advantages compared with the known process. On the one hand the move into the metastable region of the crystallisation and in the presence of electrolyte solution causes the formation of particularly large crystals, which permit a very clean separation of the oily fat fraction* Compared with the process described in the U.S. Patent No. 3*54-1,122 (crystallisation in- water) and the method shown in the German Specification No0 1,915298 (crystallisation in wetting agent solution) , there can be obtained by the new way of crystallisation in the presence of electrolyte solution here shown, for example from tallow fatty acids, a purer, i.e. of higher value crystallised fat, the stearin.. At the same time the yield of the oily fat phase, the olein, thereby rises.

On the other hand the difficulties with foaming occurring in the known process of evaporation cooling in the presence of wetting agent are avoided, since during the evaporation cooling in the presence of electrolyte solution a complete degassing of the fat mixture used is effected.. A speci; pre-treatment of the fat mixture or the introduction of a further apparatus stage in the process on continuous operation is consequently omitted. On the other hand the process according to the invention also proceeds very favourably from the a-pparatus side, since special cooling devices, such as ref igerators, scraper coolers and the like become superfluous. 0bvious3.y, however, a combination of the conventional cooling process with the new process described is feasible, but such combinations as a rule have no importance on account of their lack of economy.

Examples; lc Separation of a fatty acid mixture 500 litres of liquid undistilled split fatty acid from beef tallow (tallow A - split fatty acid) with an iodine value of 60 were placed together with 350 litres of electrolyte solution { 2% magnesium sulphate solution) in a vacuum evaporator crystalliser (tubular container of 2 m^ effective contents) at a temperature of 50°Go The container was evacuated by means of a steam je unit.

The liquid present in the evaporator was cooled by the evaporation of the water. On going below the crystallisation temperature (38°C) of the split fatty acid, stearic acid crystall ised out* At 33°C the further crystallisation of the fatty acid in the presence of pure electrolyte solution was interrupted, since at this temperature a viscous crystal slurry had already formed, which could hardly be stirred.

During the further cooling from 33 ° to 20 °C, 90 litres of old dilution were continuously added to the cycle together with 5 litres of fresh wetting agent . This fed-in solution contained 5 g/litre of wetting agent (C-^ £&t y alcohol sulphate) as well as 10 g/litre of magnesium sulphate.

While continuing the water evaporation and therefore th cooling, stearin further crystallised out, a relatively watery suspension being formed - caused by the redistribution process. When the separation temperature of 2o°G was reached, the vacuum was lifted and the suspension was separated in a scoop pipe centrifuge into an olein phase and a stearin-water phase.

The stearin-water phase was heated to about 70°C in a heat exchanger, while the stearic acid crystals were melted. Finally the stearin was separated from the old dilution by allowing to settle in a separator (settling box).

The following features of quality resulted on the basis of the batch experiment described: Iodine value of stearin: 1 to 15 Iodine value of olein. 85 to 87 Turbidity point of olein: 1 to 15°C 2. Separation of a triglyceride mixture ; 500 litres of crude palm kernel fat (I.V. 15»2, acid value 17«5» sap.value 250) were crystallised in a vacuum evaporator crystalliser (tubular container of 2 m^ effective content) in the presence of 180 litres of electrolyte solution C$°/o sodium sulphate solution) according to the method of operation of Example 1, until a temperature of 2 °C was attained. The evaporation cooling was found particularly advantageous here, since no supercooling phenomena were observed, such as readily occur after the usual process (cooling in the scraper cooler) and lead to disturbance of the crystallisation process.

After reachin the above-mentioned limiting temperature 56Ο litres of an aqueous wetting agent solution with a content of 0.8% by weight of sodium-fatty alcohol sulphate and ¾¾ of sodium sulphate were added under vacuum, until a dilution proportion (fat f actions : aqueous phase) of 1 : 1.35 was obtained. On intensive mixing the redistribution process occurred with formation of a relatively watery suspension.

On continuation of the water evaporation the suspensio was further cooled to the separating temperature of 22°C and the suspension obtained, after lifting the vacuum, was separated in a scoop pipe centrifuge into an oil phase and an aqueous suspension of the crystallised fractions. The solid fat fractions were obtained by melting and allowin to settle as in Example 1» The following quality features resulted: For the oily phase: I.V. 21.3, acid value 12.6, sap.value 20 For the solid phase: I.V. 5«0, acid value 6.1, sap. alue 265 5» Separation of a fatty alcohol mixture 500 litres of a fatty alcohol mixture (I.V. 57«3) were crystallised in a 2nr vacuum pipe container in the presence of 200 litres of electrolyte solution (6% MgSO^) , up to a temperatur of 22°Go The pulpy dispersion formed was further cooled to the separation temperature of 18°C according to Example 2, with addition of ) litres of wetting agent solution, consisting of a 6% electrolyte solution (15 g of magnesium sulphate per litre of solution) and 0»55% of wetting agent (6 g of dodecyl-benayldiethylammonium chloride per litre of solution) . The watery dispersion thus formed was separated in a scoop pipe centrifuge. The quality features after the separation are as follows: Oleyl alcohol: I.V. 85.6 Stearyl alcohol: I.V. 1206 o Continuous separation of animal fatty acids In a 3-stage vacuum tubular container cascade was crystallised in two stages undistilled beef tallow fatty acid (I.V. 58<>0) in the presence of a 2% electrolyte solution (10 g magnesium sulphate per litre of solution) „ The viscous crystal slurry was pumped from the first to the second stage and from the second to the third stage by eccentric screw pumps.

X Crystallisatio XX Cooling and dilution Corresponding to an amount of old dilirtion removed from the cycle of 30%, 70% of the old dilution accumulating in the circuit was returned to the third stage, which was previously mixed with fresh wetting agent, which resulted in a total quantity of 315 litres hour of wetting agent-containing solution. This contained 5 S of f&tt alcohol sulphate per litre of solution „ The evaporated amount of water in the three crystallisers a.s well as the 30% of the old dilution to he replaced was added as electrolyte solution for the 1st stage. The water dispersion of the third stage (ratio fatty acid;: aqueous phase = 1 : lo5) was separated in a scoo pipe centrifuge *· According to Example 1 the stearin-water phase was heated in a heat exchanger to about 70°C and consequently, the stearin crystals melted and v/ere then separated "by settling in a separator,, The following quality features "based on continuous experiments resulted: I.V. of stearin: 15 to 16 I.V. of olei 85 to 87 Turbidity point of olein: 14- to 15°0

Claims (1)

1. · A process for the separation of fat mixtures into components of different melting points "by the redistribution of water process, in which the withdrawal of heat necessary for the cooling and crystallisation of the higher melting fat fractions is effected by vacuum evaporation of an aqueous phase directly in contact with the fat mixture, comprising the following measures: (a) ' Partial or complete melting of the fat mixture, (b) Addition of an aqueous non-surface-active electrolyte solution to the molten fat mixture and evaporation of a part of the v/ater of the electrolyte solution with use of a vacuum with at the same time intensive and thorough mixing until partial or complete crystallisation of the higher melting fraction is obtained, (c) Addition of wetting agent solution with dispersion of the liquid and solid fats, (d) Separation of the dispersion "by means of centrifuge into an oily phase which contains the lower melting fat fractions and an aqueous phase containing the crystallised fat fractions in dispersed form, (e) Separation of the higher melting fat fractions from the aqueous phase by filtration or by melting and subsequent centrifuging or allowing to settle. 20 A process as claimed in claim 1 in which measure (c) includes further maintenance of the vacuum and continuation of the evaporation of water until the separation temperature is reached. 3» A process as claimed in claim 1 or claim 2 in which the crystallisation is carried out in the metastable region of the crystal formation along the vapour pressure curve of the water. " -e A process as claimed in any one of claims 1 to 3 which is operated either by the batch process or continuously. 5>. A process as claimed in any one of claims 1 to 4 in v/hich the wetting agent solution is added on reaching the limiting temperature of the crystallisation, and after the redistribution by means of evaporation cooling is further cooled until the separation temperature is reached. 6. A process as claimed in any one of claims 1 to 5 in which on reaching the separation temperature the suspension present is separated by means of scoop pipe centrifuges into an oil phase and an aqueous phase containing the solid fat fractions in suspension. 7» A process as claimed in any one of claims.1 to 6 using an electrolyte solution containing 0.1 to 10% by weight of a water-soluble chloride, sulphate or nitrate of a monovalent to trivalent metal. Qo A process as claimed i claim 7 i which, the electrolyte solution contains 0.5 to 2?/0 by weight of the chloride, silphate or nitrate. 9o Λ process as claimed in any one of claims 1 to 8 using an electrolyte solution containing sodium sulphate, magnesium sulphate or aluminium sulphate. 10» A process as claimed in any one of claims 1 to 9 using a wetting agent solution containing anionic or non-ionic water-soluble wetting agents. 11* A process as claimed in claim 1 and substantially as hereinbefore described with reference to any one of the Examples.